1. Field of the invention
The present invention relates to an electronic device.
The present invention further relates to a method of manufacturing an electronic device.
The present invention still further relates to a display panel.
2. Related Art
A field-effect transistor (FET) is a type of transistor that relies on an electric field to control the shape and hence the conductivity of a ‘channel’ in a semiconductor material. The semiconductor material may be an inorganic material, for example a silicon based semiconductor material, for example in the form of amorphous silicon, microcrystalline silicon, or it can be annealed into polysilicon. Other inorganic semiconductor materials are for example compound semiconductors such as cadmium selenium (CdSe) and metal oxides such as Zinc Oxide. Alternatively organic semiconductors may be applied, for example molecular organics, such as pentacene and TIPS and polymer semiconductors such as thiophene.
A thin film transistor (TFT) is a special kind of field effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. Thin film transistors are in particular applied for display purposes, due to their low cost and large area processibility. Unfortunately, thin film field-effect transistors show instable behaviour due to their small carrier-injection area and large dielectric-semiconductor interface. Such instabilities lead to shifts in the off-voltage, defined as the gate voltage at which the source-drain current drops below 100 pA, and non-linear contact effects (due to e.g. current crowding at points of injection). Both of these effects influence current stability and reproducibility, which will become critical in backplanes that drive high power front-planes such as organic light emitting devices. This is a known issue in traditional active matrix backplanes and is usually remedied by using several TFTs in parallel per pixel to average the effect of TFT variation, or by compensating these instabilities. Both solutions result in a more complicated design.
A static induction transistor is a vertically structured transistor used in high frequency/high power applications. Static induction transistors are used in high power, high speed and low noise applications, and in applications requiring high degree of linearity. A static induction transistor has an increased injecting area and contrary to the TFT, dielectric-semiconductor interfaces are absent. Therewith a stable behaviour is enabled. As compared to a thin film transistor, a static induction transistor has a low on/off ratio, which is a disadvantage if the transistor has to be used as a switching element.
Summarizing both types of transistors have advantages and disadvantages. In a circuit design some functions may best be performed by a thin film transistor, while other functions may best be performed by a static induction transistor. Accordingly, there is a need to provide an electronic device in which these types of transistors are integrated, as well as a need to provide an efficient way to integrate both types of transistor in such an electronic device.
It is noted that Watanabe et al. describe in “Flexible organic static induction transistors using pentacene thin films”, Appl. Phys. Lett. 87, 223505, (2005), a method of manufacturing a static induction transistor which may be used as a driver in a flexible sheet display. The fabrication process described therein is as follows. First, a 100 nm pentacene thin film is deposited on the indium tin oxide (ITO) formed on the flexible PEN substrate. Second, a slit-type Al gate electrode with a thickness of 30 nm is formed on the pentacene film. Third, the Al gate electrode is covered with a second 100 nm pentacene film. Finally, the drain Au electrode is fabricated on the pentacene film. This method requires that twice a patterned semiconductor layer is applied. Furthermore the presence of insulating layers separating source, gate and drain layers is necessary in practice to connect the SIT to other components.